shock wave

Schlieren photograph of supersonic flow over a blunt
object. The shock wave is approximately parabolic, and detached from
the object. Credit: Avco Everett Research Laboratory, Inc.

A surface or sheet of discontinuity (i.e., of abrupt changes in conditions)
set up in a supersonic field or flow, through
which the fluid undergoes a finite decrease in velocity accompanied by a
marked increase in pressure, density, temperature, and entropy.

Shock waves (also known as shocks) are caused by objects moving at supersonic
velocities. Because the surrounding fluid can propagate disturbances only
at the local speed of sound, the
moving object piles up the disturbances it is causing into a V-shaped wake
attached to the object. The supersonic boom of an aircraft is the passage
of this shock wave past the eardrum.